Power Electronics and Switch Mode Power Supply
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Transcript of Power Electronics and Switch Mode Power Supply
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Power Electronics and Switch Mode Power Supply
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Objectives
• Understand the basic principle of Power Supply Unit
• Study Series and Shunt Regulators
• Know what are the implications of Power supply
• Study Linear Regulator
• Know the power supply specifications
• Understand the block diagram of SMPS
• Explore Heater as SMPS
• Compare SMPS and Linear Supplies
• Study Buck and Boost Types of Switch-mode regulators
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Basic Principles of PSU Circuits
• Power Supply :
Provides power with the characteristics required by the load
Block diagram of PSU
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Dissipative Power Supplies
• Regulation by a conversion of excessive power to heat
• Converts heat with either a series or a shunt element
• Series Regulators:
• Shunt Regulators:
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Dissipative Power Supplies
• Vin = Vo * (1 + SQRT (1-a)) / a Where, • a = 1-tolerance • R2 = a * (Vin – Vo) / Imax• Imax = Maximum load current
• Shunt Regulators :
• Implications of Power Loss :
Equal Thermal Density Vs Efficiency
• Three systems with the same electronic load with power supplies of three different efficiencies, 35%, 65%, and 83%.
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Linear Regulator
Output voltage Vo = Vi (R2/R1 + R2)• Linear Regulator (a) :
(a) (b) (c)
• Passive Linear Regulators (b) : Vo = Vz – Vbe
• Active Linear Regulators (c) Vo = Vref (R4 / R5)
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Linear Regulator• Advantages:
– Extremely low ripple and noise– Tight regulation– Fast Transient Response – No RFI and EMI
• Disadvantages:– Efficiency Main regulator 45% – Large heat sink required– Lower power supply density– Cost and efficiency are the limitations for high current
applications
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Power Supply Specifications
• DC Output Voltage(s) VO (range)
• DC Output Current(s) IO (range)
• Load regulation % or mV• Line Regulation % or mV• Ripple / Wideband noise mV• Temperature Coefficient µV
per º C• Load Transient Recovery time
µs• Short Circuit protection SCP• Over voltage protection OVP
• Under voltage protection• Temperature Rating 0 – 17 º C or
-55 to 100 º C• RFI suppression +EMI shielding• DC output isolation• Input voltage range• Size and shape• Weight• Connectors• Turn on / turn off spikes• Voltage rate-of-rise at turn on• Vibration resistance• Shutdown mode supply current
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Common parameters
• Input Range :
For 110V AC current, an input range of 90V – 135VFor a 220V current, a range of 180V – 270V
• MTBF and MTTF :
Mean Time between Failure (MTBF) and Mean Time to Failure (MTTF) are the two parameters related to the failure of the power supply
• Peak Inrush Current :
Greatest amount of current drawn by the power supply at a given moment immediately after it is turned on
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Common parameters
• Transient Response :
Amount of time taken by a power supply to stabilize the output power levels after a device in the system starts or stops drawing power
• Load Current :
Maximum load current
Minimum load current
• Hold-up Time : Amount of time that a power supply can maintain output within the specified voltage ranges after a loss of input power
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Common parameters
Trip points for each output at which the power supply shunts down
• Over-voltage Protection :
Change in the voltage for a particular output as it transitions from its minimum load to its maximum load (or voce versa)
• Load Regulation :
Change in the output voltage as the AC input voltage transitions from the lowest to the highest value of the input range
• Line regulation :
• Efficiency : Ratio of power input to power output expressed in terms of percentage
• Power Density : Defined as watts per cubic inch
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Common parameters
• Dimension :Physical dimensions and can be given in inches (in) or millimeters (mm)
• Weight : Specified in pounds (lb) or kilograms (kg)
Fan Size
Fan Bearing Type
Voltage
Capacity
• Fan Characteristics :
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SMPS Block Diagram
• Functional Block Diagram of SMPS :
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Switching Mode Power Supplies
• Heater :
Heater schematic Heater Waveform
• Duty Cycle = Ton / (Ton + Toff)
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Linear and SMPS Comparison
• Efficiency :
Efficiency comparisons between series pass and switch mode power supply
• Cost :
Cost comparison between series pass and switch mode power supply
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Linear and SMPS Comparison
• Volume / Weight :
Volume / Weight comparison between series pass and SMPS
• Adjustable Frequency :
Switch mode allows adjusting the frequency from 1 to 300 kHz
• Flexibility :
SMPS more flexible due to capability of adjusting frequency
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Linear and SMPS Comparison
• Noise :
Noise comparison between series pass and SMPS
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Linear and SMPS Comparison
• 20 KHz Switcher Vs Linear Performance :
Parameter Switcher Linear
Efficiency 75% 30%
Size 2.0 W / in3 0.5 W / in3
Weight 40 W / lb 10 W / lb
Cost (200 – 500 W) $ 1.00 / W $ 1.25 / W
Cost (50 – 150 W) $ 1.50 / W $ 1.50 / W
Line and Load Regulation
0.1 % 0.1%
Output Ripple Vp-p 50 mV 5.0 mV
Noise Vp-p 50 – 200 mV 20 mV
Transient Response 1 ms 20 µs
Hold-up Time 20 – 30 ms 1 – 2 ms
Design Complex Simple
Power Density High Low
Input Line Filter Required Not-required
EMI High Low
• Transient Response :
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Linear and SMPS Comparison
• Advantages:
Offer better energy control
Less Weight
Higher density (Watts / in3 )
Provide modularization
Provides additional alternatives to optimize audio design circuitry
•Disadvantages:
EMI filtering &shielding is required
Noise
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Summary
• A Power Supply– a buffer circuit or Electronic Device that provides power
with the characteristics required by the load from a primary source with characteristics incompatible with the load
• Dissipative regulators – Conversion of excessive power to heat
• Linear Regulator – A voltage divider circuit
• SMPS – Minimal power loss during power conversion
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